In related experiments it has been shown that certain specific tissues (bone marrow and lymphatic tissues) are protected from x-radiation injury by prior treatment with estrogenic hormones. However, the specificity of this hormonal protective effect has not yet been determined. In the investigation funded by MBS funds we propose to determine the specificity of the hormonal protective effect and thus determine the effectiveness of the use of the hormone, 17a-ethynylestradiol, and ionizing radiation in cancer therapy. Other hormones will also be tested for their ability to produce similar effects.